"I have a keshten." (Usually a bedtime delaying tactic, or the prelude to a LONG story!)

". . . gibberish. . ." (He still uses quite a bit of gibberish when he is very excited to tell about something. Real words can be heard in between.)
Izzy-isms
"Puh-WEEZE!" (She usually says a very sweet pweeze, but when it is really, really important she busts this out!)

"I said OKAY!" (When she is being scolded, she says this which loosly translates to "I've already stopped listening to you, now give me what I want.")

"Boo-Boo Kitty" ( Hello Kitty)

That's all I can think of for now, I just didn't want to forget these!